ORIGINAL RESEARCH INTERVENTIONAL

In Vitro and In Vivo Imaging Characteristics Assessment of Polymeric Coils Compared with Standard Platinum Coils for the Treatment of Intracranial

P. Mordasini, A.K. Kraehenbuehl, J.V. Byrne, S. Vandenberghe, M. Reinert, H. Hoppe, and J. Gralla

ABSTRACT BACKGROUND AND PURPOSE: Conventional platinum coils cause imaging artifacts that reduce imaging quality and therefore impair imaging interpretation on intraprocedural or noninvasive follow-up imaging. The purpose of this study was to evaluate imaging charac- teristics and artifact production of polymeric coils compared with standard platinum coils in vitro and in vivo.

MATERIALS AND METHODS: Polymeric coils and standard platinum coils were evaluated in vitro with the use of 2 identical silicon models coiled with a packing attenuation of 20% each. DSA, flat panel CT, CT, and MR imaging were performed. In vivo evaluation of imaging characteristics of polymeric coils was performed in experimentally created rabbit carotid bifurcation aneurysms. DSA, CT/CTA, and MR imaging were performed after endovascular treatment of the aneurysms. Images were evaluated regarding visibility of individual coils, coil mass, artifact production, and visibility of residual flow within the aneurysm.

RESULTS: Overall, in vitro and in vivo imaging showed relevantly reduced artifact production of polymeric coils in all imaging modalities compared with standard platinum coils. Image quality of CT and MR imaging was improved with the use of polymeric coils, which permitted enhanced depiction of individual coil loops and residual aneurysm lumen as well as the peri-aneurysmal area. Remarkably, CT images demonstrated considerably improved image quality with only minor artifacts compared with standard coils. On DSA, polymeric coils showed transparency and allowed visualization of superimposed vessel structures.

CONCLUSIONS: This initial experimental study showed improved imaging quality with the use of polymeric coils compared with standard platinum coils in all imaging modalities. This might be advantageous for improved intraprocedural imaging for the detection of compli- cations and posttreatment noninvasive follow-up imaging.

ABBREVIATION: FP-CT ϭ flat panel CT

fter the International Subarachnoid Aneurysm Trial (ISAT) signs of recanalization in their further course,2-5 which is more Astudy,1 endovascular treatment of cerebral aneurysms with likely to occur in large or giant and wide-neck aneurysms.6,7 As a the use of platinum coils has become the main treatment tech- result, routine posttreatment imaging follow-up for coiled aneu- nique for cerebral aneurysms in most of the centers worldwide. rysms is mandatory to detect re-growth and to determine the need However, approximately 20% of coiled aneurysms demonstrate for re-treatment. However, current coil systems are made of platinum alloy, which is prone to artifact production during imaging. Imaging Received November 14, 2012; accepted after revision February 23, 2013. artifacts induced by platinum coils may significantly reduce im- From the Institute of Diagnostic and Interventional Neuroradiology (P.M., J.G.) and Institute of Diagnostic, Pediatric, and (H.H.), Inselspital; aging quality and influence interpretation of noninvasive fol- Department of Neurosurgery (A.K.K., M.R.); and ARTORG Center for Biomedical low-up imaging with the use of MRI/MRA preventing adequate Engineering Research (S.V.), University of Bern, Bern, Switzerland; and Neurovascu- lar and Neuroradiology Research Unit (J.V.B.), Nuffield Department of Surgery, The diagnosis of residual intra-aneurysmal flow and areas close to the John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom. treated aneurysm. Furthermore, extensive metal-induced beam- P.M. was supported by a scientific grant from the Swiss Foundation for Grants in Biology and Medicine (SFGBM). hardening and streak artifacts deteriorate imaging quality and Please address correspondence to Pasquale Mordasini, MD, MSc, Department of significantly impair the diagnostic accuracy of postprocedural CT Diagnostic and Interventional Neuroradiology, Inselspital, University of Bern, Freiburgstr 4, CH-3010 Bern, Switzerland; e-mail: [email protected] scans, important for the recognition and management of compli- Indicates open access to non-subscribers at www.ajnr.org cations, such as re-bleedings and aneurysm rupture during endo- Indicates article with supplemental on-line table vascular treatment. Moreover, even during endovascular treat- http://dx.doi.org/10.3174/ajnr.A3589 ment procedures, coil artifacts may impair the ability to optimally

AJNR Am J Neuroradiol 34:2177–83 Nov 2013 www.ajnr.org 2177 Embolic Devices: Polymeric Coil System and Standard GDC-18 Coils The detachable polymeric coil system (cPAX; NeuroVasx, Maple Grove, Min- nesota) was approved in 2011 by the US Food and Drug Administration for the treatment of large intracranial aneu- rysms. The coil system consists of a proximal shaft and a distal section of de- tachable polymeric strand (65 cm long, 0.018-inch outer diameter) with an in- ner lumen to introduce the delivery/de- tacher device. The polymeric strand has tantalum incorporated within to gain radio-opacity to assist during navigation and placement under fluoroscopy. The shaft has an ink mark to indicate when fluoroscopic guidance is required. A manifold with a rotating hemostatic valve is attached at the proximal end for flushing the coil system before use and FIG 1. A, Schematic illustration of the polymeric coil system (above) and the delivery/detacher to introduce the delivery/detacher de- device (below). The coil system consists of a proximal shaft (open arrow, ink marker) attached to a hemostatic valve and a distal 65-cm-long radiopaque polymeric strand with an outer diameter vice. The delivery/detacher device is a of 0.018 inch (asterisk). The delivery/detacher device (total length, 270 cm) is introduced through 0.011-inch microwire device consisting the hemostatic valve into the inner lumen of the coil system. The delivery/detacher device of a core with an electric lead wire at- consists of the microwire (arrowhead) and the heater coil attached to its distal tip (arrow). B, Fluoroscopy of an in vitro silicon aneurysm model showing the radiopaque polymeric strand tached to a heater coil at its distal end. It (black asterisk) within the microcatheter placed in the aneurysm (microcatheter tip, open arrow) is intended for the delivery of the poly- and its unfolded distal part within the aneurysm sac (white asterisk). Note the radiopaque section mer strand into the aneurysm and sub- of the heater coil (arrow) at the distal tip of the delivery/detacher device (arrowhead) running within the coil strand. The polymeric strand can be detached at any point by advancing the sequent thermal detachment. The distal radiopaque section of the heater coil at the level of the microcatheter tip and activating the end of the device is radiopaque to assist thermal detachment. C, Photographic depiction of the silicon aneurysm model after introduction in guidance and placement of the device of the polymeric coil. under fluoroscopy. The delivery/de- tacher device is packaged within the lu- visualize the vessel anatomy on DSA by superimposing vessel men of the coil system and can be moved within the inner lumen to structures of interest, such as branches arising from or close to the assist navigation of the strand for deployment within the aneurysm. aneurysmal neck, especially in larger aneurysms and aneurysms The proximal end of the delivery/detacher device consists of an elec- with a complex anatomy.8-16 trical connector, which is connected via a jumper cable to a power Therefore, from an imaging point of view, the optimal coil supply box for detachment. The polymeric strand and the delivery/ material should be the least prone to imaging artifacts as possible detacher device within it are delivered into a cerebral aneurysm to permit optimal visualization of the vessel anatomy and adja- through a standard 0.021F microcatheter by use of the same delivery cent brain tissue for endovascular treatment as well as for fol- technique as the currently used platinum coil technology. The strand low-up imaging. Metal-free, polymeric material potentially offers is fully retrievable before detachment. Thermal detachment can be the ability for reduced artifact production compared with plati- accomplished at any point along the polymer strand by placing the num. To date, only limited data about polymeric-based emboli- heater coil under fluoroscopic control at the tip of the microcatheter. zation material for endovascular treatment of cerebral aneurysms The strand design of the device and the thermal detachment by use of are available in the literature.17-19 the heater coil within the strand allow continuous filling of the aneu- The purpose of this study was to evaluate the imaging charac- rysms and detachment at any point versus the fixed detachment zone teristics and artifact production of a polymeric coil system for the of a standard platinum coil (Fig 1). treatment of intracranial aneurysms compared with standard To compare imaging characteristics with standard platinum platinum coils. coils in vitro with a comparable diameter, GDC-18 coils (0.018- inch outer diameter; Boston Scientific/Stryker Neurovascular, MATERIALS AND METHODS Natick, Massachusetts) were used for embolization of an identical We compared the imaging characteristics of standard platinum silicon model in standard coiling technique. coils and polymeric coils in vitro with the use of a silicon model, with DSA, flat panel CT (FP-CT), CT, and MR imaging. Further- In Vitro Experimental Setup more, imaging characteristics of polymeric coils were assessed in Two identical commercially available silicon models of a large vivo with the use of an experimental rabbit carotid bifurcation wide-neck right internal carotid artery aneurysm (diameter, 23 aneurysm model, with DSA, CT, CTA, and MR imaging. mm; neck, 5.7 ϫ 8.2 mm; Elastrat, Geneva, Switzerland) were 2178 Mordasini Nov 2013 www.ajnr.org used for coiling with polymeric coils and standard platinum coils. Both aneurysms were coiled up to a calculated packing attenua- tion of 20% each. Calculation of packing attenuation was per- formed with the use of an on-line cerebral aneurysm calculator software (www.angiocalc.com) with a 2D spherical function with a diameter of 23 mm for aneurysm volume calculation. The sili- con aneurysm models were connected for imaging to a pulsating circulatory pump (Medos VAD; Medos Medizintechnik AG, Stol- berg, Germany) with a frequency of pulsation of 80 beats per minute, a flow volume of 300 mL/min, and a systolic speed of 80–100 cm/s. Imaging Protocol DSA was performed in a clinical angiography suite (Axiom Artis z; Siemens, Erlangen, Germany) with the use of 10-mL hand injec- tions of iodinated contrast material (Iopamiro 300; Bracco, Mi- lano, Italy). On the table, noncontrast FP-CT (DynaCT, Siemens) was performed for the in vitro experiments with the use of the following parameters: 20-second acquisition, 0.4° increment, 512 ϫ 512 matrix, 220° total angle, 20°/s, and 15 frames per second. MRI was performed with the use of a 3T clinical MR scan- ner (Magnetom Trio, Siemens) with a 32-channel head coil (Siemens). Imaging was performed with a routine scanning protocol by use of a 3D TOF sequence (TR, 22; TE, 3.9; flip angle, 18; matrix, 384 ϫ 224; FOV, 166 ϫ 200; voxel size, 0.5 ϫ 0.5 ϫ 0.6 mm), T2 (TR, 5470 ms; TE, 81 ms; matrix, 512 ϫ 314; FOV, 180 ϫ 180 mm), T1 (TR, 250 ms; TE, 3 ms; matrix, 224 ϫ 512; FOV, 180 ϫ 180 mm), and, in addition, B0 (TR, 488 ms; TE, 5.2 ms; matrix, 64 ϫ 64; FOV, 192 ϫ 192 mm) and true fast imaging with steady state precession (TR, 4.4; TE, 2.2 ms; ma- trix, 256 ϫ 256; FOV, 200 ϫ 200) sequences in the in vitro experiments. CT and CTA were performed by use of an 8-row multide- tector clinical CT scanner (LightSpeed Ultra, GE Healthcare, Milwaukee, Wisconsin). CT was performed with the use of the following parameters: 140 kV; 70 mAs; section thickness, 1.25 FIG 2. DSA of the in vitro silicon aneurysm model coiled with a cal- mm; table increment, 2.01 mm; FOV, 250 ϫ 250. CTA in the in culated packing attenuation of 20%. Note the transparency of the vivo experiment was carried out by use of hand injection of 10 polymeric coils (C) with persistent visualization of the superimposed vessel anatomy, which is completely obscured by standard platinum mL of iodinated contrast (Iopamiro 300) through the groin coils (A). Fluoroscopic images show the difference in radio-opacity of sheath left in place for imaging after the coiling procedure. polymeric (D) and standard platinum coils (B). CTA was triggered visually on a transverse section of the de- scending aorta at the level of the heart when contrast media modification of the venous pouch aneurysm model to create an- opacification became visible. eurysms Ͼ10 mm in diameter. In brief, a venous pouch was cre- Postprocessing was performed on a workstation for viewing ated from a 1- to 1.5-cm-long section of the jugular vein. The right and creation of multiplanar reformatted images (Syngo Work- common carotid artery was temporarily clipped, and an oval ar- place, Siemens). teriotomy was performed. The left common carotid artery was temporarily clipped proximally and permanently ligated distally. Experimental Aneurysm Creation: Animal Model The left common carotid artery was then cut proximally to the All procedures were performed according to local regulations and ligature. The proximal part of the left common carotid artery was were approved by the responsible local authorities. Experimental mobilized to the right side to create an end-to-side anastomosis of bifurcation aneurysms were surgically created in 4 female adult the left-to-right common carotid artery to the proximal part of New Zealand White rabbits (3–4.5 kg). All animals were anesthe- the arteriotomy by use of single-knot 10–0 nylon sutures. The tized with an intramuscular injection of ketamine (65 mg/kg) and venous pouch was finally sutured into the resulting arteriotomy xylazine (5 mg/kg) 30 minutes before surgery, which was repeated defect in this artificial vessel bifurcation (Fig 6 A, -B). Four weeks if necessary during the procedure. Carotid bifurcation aneurysms after surgery, the aneurysms were embolized through a 5F sheath were surgically created as previously described,20 by means of a in the right femoral artery as completely as possible with poly- AJNR Am J Neuroradiol 34:2177–83 Nov 2013 www.ajnr.org 2179 FIG 3. Flat panel CT images of standard platinum coils (A and B) and polymeric coils (C and D). Note significant artifact reduction of poly- meric coils compared with standard platinum coils; however, visual- ization of the peri-aneurysmal area is still significantly impaired. meric coils. DSA, CT, CTA, and MR imaging were performed immediately after endovascular treatment. The animals were eu- thanized immediately after the experiment by a lethal injection of sodium pentobarbital (400 mg/kg intra-peritoneally).

Evaluation Criteria The images from the in vitro DSA were qualitatively evaluated for transparency and visibility of superimposed vessels (visible, not visible). The FP-CT, CT/CTA, and MR images were evaluated for artifact production (none, minor, major), visibility of individual coils, coil mass, residual aneurysm, and peri-aneurysmal area for diagnostic value (not acceptable, acceptable, excellent). All scores FIG 4. CT scan of standard platinum coils (A and B) and polymeric were assessed in consensus by the authors (P.M. and J.G.). coils (C and D). Note significant reduction of beam-hardening artifacts compared with standard platinum coils. In the aneurysm embolized RESULTS with polymeric coils, individual coils as well as residual aneurysm lu- men and neck (arrow) can be distinguished. Qualitative assessment scores for the in vitro and in vivo experi- ments are summarized in the On-line Table. Overall, in vitro and strated residual flow in the aneurysm sac and neck area in both in vivo imaging demonstrated reduced artifact production and coil groups; however, this was improved and rated excellent for higher scoring assessments for polymeric coils in all imaging mo- polymeric coils (Fig 5). In vivo MRI in aneurysms embolized with dalities compared with standard platinum coils. polymeric coils was able to depict the aneurysm wall and the sur- On DSA, polymeric coils demonstrated transparency that per- rounding soft tissue without obscuring susceptibility artifacts by mitted visualization of superimposed vessel structures in vitro use of T1WI and even more accurately delineated on T2WI (Fig and in vivo, whereas platinum coils were not transparent and 6). Remarkably, CT images demonstrated considerably improved completely masked superimposed vessel structures because of image quality with only minor artifact production compared with their high radio-attenuation (Figs 2 and 6). Polymeric coils standard platinum coils. Depiction of the embolic mass, individ- showed satisfying radio-opacity and visibility under fluoroscopy ual coils, and the peri-aneurysmal area on CT and residual intra- for safe and controlled endovascular coil delivery. FP-CT in vitro aneurysmal flow on CTA was considered acceptable for diagnos- demonstrated improved image quality as the result of reduced tic purposes by use of polymeric coils. On the other hand, CT artifact production by use of polymeric coils compared with stan- image quality with the use of standard platinum coils was not dard platinum coils. However, the image quality was still not of acceptable because of extensive beam-hardening and streak arti- full diagnostic value for both coil materials because of massive facts that obscured the area of interest (Figs 4, 6, and 7). beam-hardening and streak artifacts (Fig 3). Image quality of CT and MR imaging was improved by use of polymeric coils, which DISCUSSION permitted enhanced depiction of individual coil loops and resid- has become a well-established and increas- ual aneurysm lumen as well as the peri-aneurysmal area (Figs 4 ingly performed treatment technique for ruptured and unrup- and 5). Susceptibility artifacts in vitro on B0 images were not tured intracranial aneurysms.1 However, because of the risk of visible with the use of polymeric coils. TOF imaging demon- aneurysm re-growth and neck recurrence after coil treatment, 2180 Mordasini Nov 2013 www.ajnr.org FIG 5. MR images and corresponding DSA of standard platinum coils (upper row) and polymeric coils (lower row) in vitro. Less magnetic field distortion and artifact production are seen with polymeric coils with the use of MRI. Individual coils can be distinguished in T2WI, TRUFI (true fast imaging with steady state precession), and TOF images as compared with standard coils. Note the visualization of residual flow within the aneurysm sac and the neck area in the aneurysm treated with polymeric coils in the TOF and DSA (arrows) compared with standard platinum coils at the same packing attenuation.

encouraging imaging quality and improv- ing artifact reduction of MRI/MRA, disad- vantages of this technique include com- paratively long examination time, limited availability, and contraindication for pa- tients with pacemakers and biostimula- tors. Metallic implants cause massive beam-hardening and streak artifacts on CT images, which deteriorate image qual- ity and furthermore superimpose other brain structures of interest. The metallic nature of standard platinum coils pre- cludes the use of CT or CTA as imaging techniques after coil treatment.26,27 Therefore, from an imaging point of view, an optimal coil material would permit ar- tifact-free imaging or cause the least possi- ble imaging artifacts and would allow reli- able and accurate imaging diagnosis. Polymeric-based coil material has the po- FIG 6. DSA demonstrates the anatomy of the venous patch carotid artery bifurcation model with the tential to offer these features. However, to anastomosis of the left carotid artery proximal to the aneurysm (A and B). Posttreatment DSA (B) and 3D rotational angiography (C) show complete obliteration of the aneurysm (B). Note the persistent date, only limited data about metal-free visibility of the right carotid artery despite superimposition by the coil mass. Note the minor effect of polymeric-based embolic material for the beam-hardening artifacts on the surrounding soft tissue on CT imaging (D). MR images demonstrate treatment of intracranial aneurysms are visibility of individual coil loops in the T2WI (E) and the lack of intra-aneurysmal flow in the TOF image (F). available. Hydrogel filaments opacified with barium sulfate or iodine have been follow-up imaging is mandatory. DSA has been used as the crite- used in experimental studies to evaluate occlusion of aneurysms on rion standard for follow-up assessment of coiled aneurysms. How- CT and CTA. These studies have shown promising results in detect- ever, diagnostic DSA is an invasive, comparatively expensive, and ing aneurysmal remnants after treatment with hydrogel filaments time-consuming procedure with the potential risk of clinical compli- and demonstrate the potential of CTA to provide images suitable to cations.21,22 To overcome the disadvantages of DSA noninvasive im- determine whether re-treatment is necessary.17-19 aging, follow-up is performed as an alternative. Imaging artifacts caused by the metallic nature of coils are an important factor influ- The present study, through the use of different imaging mo- encing the quality of posttreatment imaging. MRI/MRA has been dalities, has demonstrated that polymeric coils cause less imaging increasingly used as the imaging technique of choice for posttreat- artifacts compared with standard platinum coils on all imaging ment follow-up of coiled aneurysms.9,11,15,16,23-25 However, despite modalities. Overall, they provided better imaging and visualiza- AJNR Am J Neuroradiol 34:2177–83 Nov 2013 www.ajnr.org 2181 caused by insufficient visualization of crucial anatomic information must be accepted to avoid inadvertent vessel occlusion. Furthermore, DSA has been shown to be less accurate in detecting aneurysm body remnants extending or invaginating into the coil mass. Coils sur- rounding the aneurysmal remnant form a radio-attenuated, helmet- like mass around the remnant, causing difficulties in delineating the remnant, a phenomenon previously referred to as the helmet effect.16 The DSA examinations in the current study have demonstrated ex- cellent visibility of superimposed vessel structures through the coil mass during and after coiling. This feature may improve procedural safety and efficacy of the treatment or re-treatment of complex and large to giant cerebral aneurysms. On the other hand, reduced radio-opacity of the polymeric coil system might also cause potential disadvantages in the clinical setting. Visual assessment and determination of ade- quacy of coil packing and residual filling of a treated aneurysm might be more difficult to judge as compared with platinum FIG 7. CT images of a coiled carotid bifurcation aneurysm. Note coils because of the better appreciation of these findings. Fur- the reduced artifact production and visibility of individual coils on the unenhanced CT scan (A and B). CTA shows complete occlusion of the thermore, the polymeric coils are less fluoroscopically visible aneurysm and minimal artifact production (C and D). than platinum coils, and overlapping bone and soft tissue structures might further impede intraprocedural visibility. tion of the coil mass, coil details, and the soft tissue area adjacent Last, because the system consists of a polymer strand without to the embolized aneurysm. Therefore, polymeric coils might be preformed loops, it must bend at the aneurysm wall to adapt to able to improve posttreatment surveillance as well as detection the aneurysm geometry, which makes the system more rigid to and avoidance of peri-procedural complications. place within an aneurysm compared with similar-sized plati- MRI examinations in vitro as well as in vivo have demon- num coils. strated excellent visualization of details of the coil mass and indi- Although the present experimental study has shown promis- vidual coils. With the use of TOF sequences, the presence of re- ing imaging characteristics of polymeric coils and potential impli- sidual flow within an embolized aneurysm was visible, a feature of greatest significance for follow-up imaging of coiled aneurysms. cations for clinical management, it has its inherent limitations. The lack of susceptibility artifacts demonstrated on B0 images First, only a small sample of in vitro and in vivo imaging was permits artifact-free imaging of soft tissue structures immediately performed and qualitatively analyzed. The study was conducted adjacent to the embolized aneurysm on T1WI and T2WI. Fur- with the aim to preliminarily evaluate the imaging characteristics thermore, detailed depiction of the aneurysm wall could be and artifact production of a polymeric-based coil system through achieved in the experimentally created in vivo aneurysms. the use of different imaging modalities compared with standard On conventional CT, the aneurysms embolized with poly- platinum coils. Second, these preliminary imaging findings must meric coils demonstrated only minimal beam-hardening and be further investigated in experimental and clinical studies, which streak artifacts. The beam-hardening artifacts of the polymeric are lacking at the moment. Clinically significant properties such coils were significantly reduced compared with platinum coils, as potential thrombogenicity and biologic behavior of the coil with only minimal residual artifacts. The improved image quality mass as well as the durability of the treatment compared with allowed depiction of single-coil loops and residual aneurysm standard coils have not been addressed in this study. Last, the lumen. In our opinion, the residual artifacts are caused by the clinical value of reduced imaging artifacts and especially the po- tantalum added to the polymer to gain some radio-opacity for tential role of CT/CTA examinations in the acute setting and dur- visualization of the coil strand on fluoroscopy during the proce- ing follow-up of endovascular aneurysm treatment must be fur- dure. This artifact reduction may significantly improve diagnostic ther established. accuracy of posttreatment CT examinations. CT has an important role in the emergency and acute settings of subarachnoid hemor- rhage to recognize potential hemorrhagic complications and re- CONCLUSIONS bleedings, which can be masked by metallic coil artifacts. Further- This initial experimental study demonstrated improved imaging more, position of single coils and coil loops could be visualized, a quality with the use of polymeric coils compared with standard feature that is of accurate. platinum coils in all examined imaging modalities. Artifact reduc- The endovascular treatment of large and giant aneurysms may tion permits better visualization of coils and coil loops as well as still necessitate the introduction of considerably large coil masses. the surrounding soft tissue. This might be advantageous for im- Superimposition of a radio-attenuated coil mass may impair visual- proved intraprocedural imaging for the detection of complica- ization of vessel structures of interest, especially in the treatment of tions and posttreatment noninvasive follow-up imaging. Further complex aneurysms and in aneurysms with vessels arising near or at investigation and evaluation of the clinical value and imaging the aneurysm neck. In some clinical settings, incomplete treatment characteristics of polymeric embolization material is needed. 2182 Mordasini Nov 2013 www.ajnr.org Disclosures: Pasquale Mordasini—RELATED: Grant: P.M. was supported by a scien- 13. Walker MT, Tsai J, Parish T, et al. MR angiographic evaluation of tific grant of the Swiss Foundation for Grants in Biology and Medicine (SFGBM). James platinum coil packs at 1.5T and 3T: an in vitro assessment of artifact Byrne—UNRELATED: Board Membership: Codman Neurovascular, Comments: SAB production: technical note. AJNR Am J Neuroradiol 2005;26:848–53 member; Grants/Grants Pending: Balt International,* Siemens AG*; Royalties: 14. Hennemeyer CT, Wicklow K, Feinberg DA, et al. In vitro evaluation Springer-Verlag, Comments: Portion of book sales. Michael Reinert—UNRELATED: Consultancy: Oxygen Biotherapeutics.* Jan Gralla—UNRELATED: Consultancy: Co- of platinum Guglielmi detachable coils at 3 T with a porcine model: vidien–Ischemic Intervention*; Grants/Grants Pending: Swiss National Foun- safety issues and artifacts. Radiology 2001;219:732–37 dation* (*money paid to institution). 15. Gauvrit JY, Leclerc X, Caron S, et al. Intracranial aneurysms treated with Guglielmi detachable coils: imaging follow-up with contrast- REFERENCES enhanced MR angiography. Stroke 2006;37:1033–37 16. Agid R, Willinsky RA, Lee SK, et al. 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